GB2173080A - Motor driven microwave heater - Google Patents

Abstract

A motor drive for the heater in a microwave oven drives the rotation of the heater 5 by a motor 14 and controls the rotation of the motor with a control device to automatically position the heater suitably for cooking, thus preventing under or overcooking. Means are provided to permit the heater to be rotated between a vertical position opposing a convection fan 3 in the heating chamber and a horizontal position directly above a tray 4. <IMAGE>

Description

SPECIFICATION Motor drive for heater in microwave oven Background ofthe invention This invention concerns a motordrivefora heater in the heating chamber of a microwave oven, which can freely rotate the high frequency heater between a vertical position for baking and microwave cooking, and a horizontal position for broiling or grilling.

Heaters located vertically in microwave ovens, opposing a convection fan in the back of the heating chamber, with which baking and microwave cooking were effected, which could be lowered to a horizontal position directly above a tray in the heating chamber for broiling were available with conventional units.

However, with the heater in the conventional microwave oven, positioning of the heating elementwas effected by moving a heater drive lever on the control panel. With this type of positioning, food was in some cases not browned properly, orthe temperature in the oven differed from that desired if it was not positioned properly, resulting in over or undercooking of food.

Object and summary of the invention The object of this invention isto eliminate the above problems by providing a motor drive device which has a motorto rotate the heater in the microwave oven, and a control device to control the rotation ofthe motor in orderto automatically position the heater suitable to provide for no-fail cooking.

Composition and effect ofthe invention In orderto achieve the above goal, means are provided to allow rotation ofthe heater in the heating chamber ofthe microwave oven from a vertical position opposing the convection fan, to a horizontal position directly above the tray; a motor drive is provided to rotate the heater; and a control device is provided to control the rotation ofthe motor.

In the motor drive for the heater in the microwave oven in this invention which is composed of the components stated above, the control device controls the rotation ofthe motor according to the type of cooking, locating the heater in a suitable position, eliminating over or undercooking offood due to user error.

Brief description of the drawings Fig. 1 shows an overall oblique view ofthe microwave oven, which is the embodiment of this invention, fig. 2 shows an oblique outline ofthe motor drive for the heater in this microwave oven, fig. 3 a vertical sectional view of the motor drive for the heater in this microwave oven, fig. 4 and 5 are side views of the heater drive gear section to explain the operation of the motor drive, fig. 6 a block diagram ofthe control device for the motor drive for the heater in this microwave oven, and fig. 7 a flow chart showing the operation ofthe microwave oven.

Detailed description of the invention As shown infig. 1,the microwave oven (1 } is provided with a convection fan (3) on the front of the back wall ofthe heating chamber (2), and a tray (4) on the bottom of the heating chamber (2), which food to be cooked is placed on. A heater (5) which is bent back and forth is provided in the heating chamber (2), which can freely rotate by means of a pivot hole (6) provided in the side wall. This heater (5) rotates between a vertical position opposing the convection fan (3) and a horizontal position directly above the tray (4). A door (7) is provided on the front ofthe microwave oven (1), and a control panel (8) beside it.A heater up button (9), heater down button (10), grill select button (11), grill auto button (12), heating button (13) and other buttons are provided on the control panel (8).

Rotation ofthe heater (5) in the heating chamber (2) is driven by the motor (14) provided on the outside of the hole (6) in the side wall. This motor drive (14) comprises a motor (15) and transmission device (16) as shown in fig. 2 and 3. The motor (15) is an AC motor which can be reversed by the control device. The transmission device (16) transmits the rotation ofthe motor (15) to the heater. The rotation of the motor (15) is first reduced bythe small pulley (17), belt (18) and big pulley (19), and transmitted to the worm gear (20) which is on the same shaft as the big pulley (19). The rotation which has been transmitted to the worm gear (20) is reduced and transmitted to the worm wheel (21).A clutch gear (22) is mounted on the rotation shaft ofthewormwheel (21)which allowsfree rotation and sliding in the thrust direction. Clutch linings, (23), (23) with a high abrasion factorarefirmlyfixed to the surfaces ofthe clutch gear (22) andworm wheel (21) which face each other, and the clutch gear is strongly pressed againstthe worm wheel (21) by a compression coil spring (24) which is mounted on the worm wheel (21 ). The rotation that is transmitted to the worm wheel (21)is thustransmitted to clutch gear(22) at a torque transmission ratio of 1:1. The rotation that is transmitted to the clutch gear (22) is further reduced and transmitted by heater drive gear (25).The rotation that istransmitted to the heater drive gear (25) is finally transmitted to the heater (5). The heater (5) sticks out ofthe hole (6) provided in the sidewall of the shown in fig. 3, and the end ofthe heaterthat sticks out (26) is bent perpendicular with respect to the rotation shaft. A heater choke (27) to permit penetration of the heater (5) and choke insulation (28) are provided around the outside of the hole (6), which serve as a bearing for the heater (5), prevents leakage of microwaves and is double insulation for the heater (5).

A heater drive angle (29) is fixed to the heater choke (27), and the heater drive gear (25) of the transmission device (16) is mounted to the heater drive angle (29) in such a way that is can freely rotate, to be integral with the rotation shaft of the heater (5). The heater drive gear (25) is provided with a sector gear (30) with a rotation angle of 90 degrees or more, and a small projection (31) and L shaped projection with the end bent on the periphery otherthan the sector gear (30).

The sector gear (30) transmits rotation to the heater drive gear (25) by meshing with the clutch gear (22). A hole (33) is provided in the end ofthe L shaped projection (32) which is bent, and the rotation ofthe heater drive gear (25) is transmitted to the heater (5) by fitting the end ofthe heater (5) in this hole (33). The motor (15) thus drives the heater (5) through the transmission device (16). If, for example,the rpm of the motor is 5000, and the reduction ratio ofthe transmission device is 1/1000, the heater can be rotated from the vertical to the horizontal position in about 3 seconds.

A microswitch (34) to detectthe vertical position of the heater (5) and another microswitch (35) to detect the horizontal position ofthe heater (5) are provided around the rotating arc of the heater drive gear (25) as shown in fig. 4 and 5, with the small projection (31) on the heater drive gear (25) pressing against the vertical position detecting microswitch (34) to turn it ON when the heater is in the vertical position as shown in fig. 4, and the Lshaped projection (32) of the heaterdrive gear(25) pressing againstthe horizontal position detecting microswitch (35) to turn it ON when the heater (5) is in the horizontal position.

The control device controls the rotation, stopping and direction of rotation of the motor (15), comprises a CPU (37) to which a memory (36) is connected, with signals from the control keys 9-13 on the control panel (8), and signals from the vertical position detecting microswitch (34) and horizontal detecting microswitch (35) taken in fromthe I/O interface (38), and a control signal outputto the motor rotation changeover relay (39) to operate the motor (15). When the heater down button (10) is pressed, the control device drives the motor (15) in the forward direction to move the heater (5) towards a horizontal position from a vertical position.If the heater down button is released while the heater is being lowered, the rotation ofthe motor (15) stops, stopping the heater (5) atan intermediate position, permitting the heater (5) to be stopped at an arbitrary position The heater (5) is moved until the horizontal position detecting microswitch (35) is turned ON if the heater down button (10) is held. Input ofthe heater down button (10) is not accepted while the horizontal position detecting microswitch (35) is ON. When the heater up button (9) is pressed, the control device causes the motor (15) to rotate in the reverse direction, moving the heater (5) towards a vertical position from a horizontal position.The rotate ofthe motor (15) also stops when the heater up button (9) is released, stopping the movement ofthe heater (5) atan intermediate position, allowing the heater (5) to be located at an arbitrary position. If heater up button (9) is held, the heater (5) continues to move until it is stopped atthe vertical position when the vertical position detecting microswitch (34) goes ON.

Input ofthe heater up button (9) is not accepted while the vertical position detecting microswitch (34) is ON.

The operation ofthe grill auto button (12) on the control panel (8) of the microwave oven (1) will now be explained, using fig. 7.

Instep n1 (step ni (number) will be hereinafter abbreviated as ni),when the user pressesthe heater button (13), microwave heating is commenced (n2).

When microwave heating ends (n3), the control device causesthemotcr(15)to rotate in theforward direction, moving the heater (5) towards the horizontal position from thevertical position (n4). When the heater (5) stops atthe horizontal position (n5), grilling is commenced (n6). If door (7) (n7) remains closed, the control device causes the heater (5) to be moved towardsthevertical position (n9)when grilling ends (n8). When the heater (5) stops atthevertical position (n1 0), cooking is finished. Furthermore, ifthe door (7) is opened during grilling (n7X, the heater(5) isturned off (n1 1), the control device goes to n9, and the heater (5) is raised to the vertical position.This preventsthe possibility ofthe user inadvertently touching the heater (5) and burning his/her hand.

The transmission device (16) ofthe motor drive for heatertransmitsthe rotation of the motor (15) through the worm gear (20) and worm wheel (21). This prevents anyvariation in position ofthe heater (5) due to its own weight. However, in the transmission device (16) there is a slip clutch mechanism which comprises clutch linings (23), (23) fixed to opposing surfaces of the worm wheel (21) and clutch gear (22), which are held together by a compression spring (24). Rotation is transmitted through this slip clutch, so thatwhen external force is applied, the slip clutch mechanism slips, allowing the heater (5) to be moved. This prevents the heater (5) from getting in the way by allowing itto be moved to an arbitrary position when the unit is unplugged in orderto clean the inside ofthe heating chamber (2) of the microwave oven (1).

Claims (8)

1. Motor drivefor heater in microwave oven in which means are provided to permit rotation of the heater in the heating chamber from a vertical position opposing a convection fan to a horizontal position directly above a tray; a motor and transmission device are provided to drive rotation ofthe heater; and a control device is provided to control the rotation ofthe motor.

2. Motordriveforheaterin microwave oven as stated in claim (1), in which the control device permits stopping ofthe heater in an arbitrary intermediate position by operating the heater up button and heater down button provided on the control panel.

3. Motordriveforheaterin microwaveovenas stated in claim (1), in which the control device causes the motorto rotate and return the heater to thevertical position when the heating chamber door is opened, regardless of cooking status.

4. Motor drive for heater in microwave oven as stated in claim (1), in which the transmission device transmits powerthrough a spring loaded slip clutch.

5. A microwave oven having a heating element which is rotatable between first and second positions of use, the oven also having a motorto rotate the said element between the said positions and control meansforthe motor.

6. A microwave oven according to claim Sin which the heating element extends generally vertically in the firstsaid position and extends generally horizontally in the second said position.

7. A microwave oven according to claim 5 or claim 6 in which the heating element is located opposed to a fan when it is in the said first position.

8. A microwave oven substantially as herein described with referenceto the accompanying draw ings.